If so I agree there is literally no space to mount a receiver especially if it's a PWM one. What RX are you using? Hopefully it's rather small and it will fit between the camera and the flight controller, possibly removing the casing and replacing with heatshrink will help. I know the XSR receiver fits there (just).

The other option is to remove the casing on your receiver and also the pin connectors and solder the ppm/sbus cables directly to it and the Heatshrink it onto the bottom of the frame.